1. Field of the Invention
The present invention relates generally to a feed water heating system for a power-generating plant. More specifically, the invention relates to a feed water heating system for a power-generating plant, which has a steam injector for heating a feed water supplied to a nuclear reactor of a nuclear power station, a boiler of a thermal power plant or the like.
2. Related Background Art
First, the background art of the first invention will be described.
FIG. 11 is a schematic view of a power-generating plant turbine system in a power-generating plant.
The steam generated by a steam generator 1 is introduced into a high-pressure side steam turbine 2A via a main steam pipe 13 to drive the high-pressure side steam turbine 2A.
The high-pressure side steam turbine 2A is connected to a low-pressure side steam turbine 2B via a connecting pipe 14. In the middle of the connecting pipe 14, there is provided a heater 11 for heating the steam, which has done work in the steam turbine 2A, with the steam generated by the steam generator 1 or the turbine bled steam.
The steam, which has done work in the low-pressure side steam turbine 2B, is condensed at a condenser 3. The condensed water is temperature and pressure raised by means of a pressure raising pump group 15, feed water heater groups 6a and 6b and feed water pumps 5 to be returned to the steam generator 1 as a feed water.
Thus, the feed water supply system facility in the turbine system of the power-generating plant comprises a multistage, multi series, large rotating equipment, such as pressure raising pumps 15 and feed water pumps 5, and feed wafer heater groups 6a and 6b.
Then, the background art of the second invention will be described.
FIG. 30 shows a feed water heating system 300 for a current advanced boiling water reactor (which will be hereinafter referred to as an "ABWR").
In FIG. 30, a high-pressure steam turbine 102 and a low-pressure steam turbine 103 are driven by the steam generated by a nuclear reactor 101 to drive a generator 104 connected to the high-pressure steam turbine 102 and the low-pressure steam turbine 103. The steam, which has done work in the low-pressure steam turbine 103, is condensed in a condenser 105. The condensate in the condenser 105 is supplied as a feed water 109 to a feed water heating system 300 via an air ejector 107 and a condensate filter/demineralizer 108 by means of a low-pressure condensate pump 106.
The feed water 109 is temperature and pressure raised by means of the feed water heating system 300 to be fed to a high-pressure feed water heating section 111, so that a high-temperature and high-pressure feed water is supplied from the high-pressure feed water heating section 111 to the nuclear reactor 101. Reference number 310 denotes a drain tank. In addition, reference number 311 denotes a low-pressure drain pump, and 110 denotes a high-pressure condensate pump.
This feed water heating system 300 comprises three lines A, B, C of heat exchanger type heaters provided in parallel. Each of the lines A, B, C comprises four heat exchanger type low-pressure feed water heaters 301 connected in series. Thus, the feed water heating system 300 has 12 low-pressure feed water heaters 301 in all.
Bled steams 303, 304, 305, 306 extracted from the low-pressure steam turbine 103 are supplied to the four-stage series low-pressure feed water heaters 301, 301, 301, 301 of the respective lines. When the rated operation is carried out, the pressure of the first state bled steam 303 is 0.05 MPa, and the pressure of the second stage bled steam 304 is 0.1 MPa. In addition, the pressure of the third stage bled steam 305 is 0.21 MPa, and the pressure of the fourth stage bled steam 306 is 0.4 MPa. Each of the low-pressure feed water heaters 301 has a diameter of about 2 m and a length of about 14 m. As shown in FIG. 31, the low-pressure feed water heater 301 is used as a neck heater 307. Four neck heaters 307 for each line are provided on the upper portion of the condenser 105. As shown in FIG. 32, the low-pressure feed water heater 301 serving as the neck neater 307 comprises ten thousands heat-transfer pipes of stainless per one heater. Therefore, chromium, which is one component of stainless steel, is eluted as chromium ion into the feed water to enter into the nuclear reactor 101 to be adhered to equipment in the reactor, and the heat-transfer pipes themselves deteriorate, so that it is required to exchange the heat-transfer pipes every about 20 years. This exchange work requires about a half year since the neck heaters 307 must be drawn out of the upper portion of the condenser 105 to exchange the heat exchanger. The electricity rate corresponding to the quantity of electricity generated by the ABWR for a half year reaches about thirty billion yen. Therefore, it is undesirable to stop the plant for a long term in respect of costs in plant's life. In addition, since the installation height of the neck heaters 307 is added to the height of the condenser 105 by adopting the neck heaters 307, the installation height of the turbine 103 put thereon and the height of a turbine building 309 (see FIG. 29(a)) are increased.
The feed water supply system facility in the turbine system of the power-generating plant comprises a multistage, multi series, large rotating equipment, such as pressure raising pumps and feed water pumps, and feed wafer heater groups. Therefore, there is a problem in that even if the reliability of each equipment is improved, the rate of occurrence of malfunction increases necessarily as a whole since the facility has a plurality of equipment.